client/v3: clear auth token when encounter ErrInvalidAuthToken
client/v3: clear auth token when encounter ErrInvalidAuthToken

Old etcdserver which have not apply pr of #12165 will check auth token
even if the request is an Authenticate request.
If the client has a invalid auth token, it will not able to update it's
token, since the Authenticate has a invalid auth token.
This fix clear the auth token when encounter an ErrInvalidAuthToken to
talk with old version etcd servers.

Fix #12385 with #12165 and #12264

mqliang/etcd,mkumatag/etcd,mqliang/etcd,coreos/etcd,rnaveiras/etcd,mkumatag/etcd,ajityagaty/etcd,gyuho/etcd,etcd-io/etcd,mqliang/etcd,ajityagaty/etcd,mkumatag/etcd,rnaveiras/etcd,gyuho/etcd,ajityagaty/etcd,etcd-io/etcd,coreos/etcd,rnaveiras/etcd,etcd-io/etcd